1. Field of the Invention
The present invention relates generally to batteries and, more specifically, to advanced lead acid batteries used for vehicles having low cost, high specific energy, and long cycle life.
2. Description of the Related Art
It is known to provide storage batteries for vehicles for storing electrical energy for use by the vehicle. Lead acid, nickel-metal hydride, and lithium-ion batteries are three types of storage batteries for potential applications of electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (PHEV). Though lithium-ion batteries have high specific energy (Watt-hour/kilogram, Wh/kg) and have been broadly used in small electronic devices, such as cell phones and laptops, their high cost, performance, abuse tolerance and cycle life hamper them to be used in EV, HEV, and PHEV (See, Department of Energy 2009 Annual Progress Report for Energy Storage Research and Development). In addition, with present technology, it is difficult to recycle lithium-ion batteries. The cost of nickel-metal hydride batteries is high and their specific energy and cell efficiency are low although they have been used in HEV. The objectives of Department of Energy (DOE) are that by 2014 a PHEV battery should enable a 40-mile all-electric range and cost $3,400. The current cost of Li-based or Ni-based batteries is approximately a factor of three to five times too high on a kWh basis for PHEVs. The main costs for Li-based batteries are the high costs of raw materials and materials processing, cell and module packaging, and manufacturing. Therefore, it is desirable to develop new technologies to lower the costs of Li-based batteries.
Most of current automotive storage batteries are lead acid batteries due to their inexpensive, high power, reliable, and 98% recycling properties. However, the low specific energy and short cycle life of current commercial lead acid batteries resist them from being used for EV, HEV, and PHEV applications. If the specific energy and cycle life of the lead acid battery can be greatly increased, lead acid batteries should have a great advantage on other types of storage batteries. Therefore, it is desirable to develop low cost advanced lead acid batteries with high specific energy and long cycle life for EV, HEV, PHEV, and as well as other applications.
The lead acid battery has more than one hundred years of history. A lot of research on its properties has been done, and hundreds of papers, patents, and reports have been published and issued. The problems of low specific energy and short cycle life are still waiting to be solved. As is well known, low specific energy is mainly from two aspects. The first aspect is the heavy lead grids and the top lead that connects the plates and transfers electric current to and from the terminals. For example, the weight of the grids and top lead in a commercial SLI (start, light, ignition) lead acid battery is about 27% of the total battery weight, and the weight of the active materials is only about 36% of the total weight (Handbook of Batteries 3rd edition, p 23.17, McGraw-Hill). The decrease of the weight of the grids and top lead can increase the weight rate of the active materials in the battery, and then increase the specific energy. The second aspect is the low utilization of active materials. The utilization rate of active materials in a current SLI lead acid battery is about 25% to 35%. Such low utilization rate is mainly decided by the structures of the grids (Electrochemical Power Source, M. Barak, pp 196, (The Institution of Electrical Engineers, London, 1980)). The short cycle life is mainly from the positive grid corrosion and the plate sulfation, and specifically the negative grid sulfation directly results in a dead battery.
In the last decade, considerable work has been done to decrease the weight of the grids of lead acid batteries and to improve their corrosion ability. One method is to use light metals, such as aluminum, copper, iron, titanium, or their alloys, as a core, which is covered with a thin lead film/foil layer. The early work was done by Henry Walker in U.S. Pat. No. 3,884,716, in which the aluminum is used as a core coated by a lead layer and one or more thin metal bonding layers between the aluminum and lead layer are also added. The same kind of work was done by John Timmons et al. in U.S. Pat. No. 6,447,954 and Ramesh Bhardwaj et al. in U.S. Pat. No. 6,586,136 and U.S. Pat. No. 6,566,010. John Timmons et al. in U.S. Pat. No. 6,316,148 also directly encapsulated aluminum or other metals with lead foils to form the grids. Yolshina et al. (Journal of Power Sources 78, 84 (1999)) directly deposited lead layers on the surfaces of aluminum and aluminum alloys as the grids. Lun-Shu Yeh et al. in U.S. Pat. No. 4,683,648 plated a lead layer on a titanium core to form the grid. Robert Feldstein in U.S. Pat. No. 5,339,873 and U.S. Pat. No. 5,544,681 used titanium as the core covered with a lead layer by means of ion implantation. However, after limited cycles, the sulfuric acid can penetrate the thin lead coatings on the metal cores and attack the metal cores.
In addition to using light metals as the grid/plate substrates as mentioned above, polymers, glass fibers, and carbon coated by lead/lead alloys have been used to construct the grids/plates for lead acid batteries. Richard Hammar et al. in U.S. Pat. No. 4,221,854 described a light grid that comprised a substrate made of a polymer laminated with lead foil. Kensaku Tsuchida et al. in U.S. Pat. No. 6,232,017 showed that polyamide glass fibers coated by a thin lead layer were used to construct a composite grid. The light carbon/graphite grids/plates coated by lead/lead alloys have been studied by several groups, such as Elod Gyenge et al. (Journal of Power Source 113, 388 (2003)) and Kaushik Das et al. (Journal of Power Source 89, 112 (2000)). The corrosion problem of the coated lead layer is similar to what the metal cores coated by lead have. The corroded thin lead layer has very large electrical resistance, which greatly lowers the performance of the batteries. B. Hariprakash et al. (Journal of Power Source 173, 565 (2007)) reported a study in which the coated lead layer is followed by a corrosion-resistant and conductive polyaniline layer by electrodeposition. However, they found that the adhesion between active materials and conductive polymer is weak and the cell capacity decreases rapidly beyond 30 cycles due to active material shedding. Rongrong Chen et al. in U.S. Pat. No. 6,617,071 also suggested coating conductive polymers on the grid surface to reduce the corrosion of lead metal components. In addition to the weak bonding of active materials on conductive polymers, conductive polymers are very expensive.
Using graphite foam as current collectors for lead acid batteries has been widely investigated, which can greatly decrease the weight of lead acid batteries. Kurtis Chad Kelley et al. in U.S. Pat. No. 6,979,513 described a method for making the carbon foam plates used in the battery. However, the evaluation of the electrochemical stability of the carbon foam current collectors for lead acid batteries by Young-Il. Jang et al. (Journal of Power Source 161, 1392-1399 (2006)) showed that in the voltage range of the positive electrode the graphite foams are not electrochemically stable due to intercalation of sulfuric acid into graphite, and hence graphite foam is not suitable for use as positive current collector for lead acid batteries. Young-Il. Jang et al. also showed that paste adhesion is weak and the cycle performance of the battery is poor. The discharge capacity is only ˜25% of the available lead for the first cycle and decreases by half for second cycle.
Conductive melt oxides have been considered as a corrosion resistant layer. John Rowlette in U.S. Pat. No. 5,334,464 and U.S. Pat. No. 5,643,696 described adding a SnO2 layer on the lead layer to protect lead from corrosion. Naum Pinsky et al. in U.S. Pat. No. 4,787,125 and Maurice Fitzgerald et al. in U.S. Pat. No. 4,708,918 also reported that tin oxide was used as the conductive and corrosion protection layers. However, the later investigation of Wen-Hong Kao (Journal of Power Source 70, 8-15 (1998)) reveals that prolonged exposure of SnO2 in acid under positive potential results in passivation due to conversion of low valent tin or loss of the dopants. Wen-Hong Kao examined the chemical and electrochemical stability over 120 different ceramic materials, and he found that only silicides of Ti, Nb and Ta appear to be acceptable to be used in lead acid batteries. However, Wen-Hong Kao also found that the interaction/bonding between these materials and active materials is very weak, and the active materials fell off from the substrates after curing. Several methods were tried to improve paste adhesion, but the improvement is limited.
Though Wen-Hong Kao found that TiOx dissolves or decomposes in sulfuric acid, others show that titanium suboxides, TixOy, are good for anti-corrosion materials. However, as mentioned above, lacking paste adhesion is a serious problem for ceramic, TixOy, substrates. A. C. Loyns et al. (Journal of Power Sources 144, 329-337 (2005)) designed a special bipolar structure for the paste adhesion, in which the titanium suboxide composite is sandwiched between two lead alloy foils and the active materials are held by the conventional lead/lead alloy grids. Such plates are heavy, and the lead grid corrosion may damage the plates as the conventional lead acid batteries do.
Therefore, it is desirable to provide a new current collector and lead acid battery for vehicle applications. It is also desirable to provide a current collector and lead acid battery having a relatively low cost, high specific energy, and long cycle life. It is further desirable to provide a current collector and lead acid battery having improved mechanical properties. Thus, there is a need in the art to provide a current collector and lead acid battery that meets at least one of these desires.